Allies: Love 'em. Mix and match, baby!
2 x FoC at 2k: Not sure yet how I feel, I have yet to actually try this. My... gut sense is that this isn't that big of a deal, that it will help weaker codices more than the stronger codices, and that if you've ever played at a doubles tournament with 2 x 1000 point allied armies... you've already played with this.
Hull Points: Makes us change our game, but I love em (makes heavy armor more meaningful, which is a good thing).
Flyers: Very cool concept, very solid rules... NO DAMNED WAY TO KILL THEM! I mean, you CAN kill a couple of them, with weight of fire. But facing 6 of them... no fucking way without flyers of your own. I have downed Vendettas with twin linked Psycannons and Twin Linked Psyflemen, but it takes the entire army focussing to take down one per turn. Simply not a good balance of ways to take them down other than other flyers BUT if they go too far and give everything Skyfire it makes them worthless. A tough thing to balance. My sense is to give purchasable Skyfire upgrades for things like vehicles and Missiles but for a significant cost... The FAQs were dissapointing in this regard.
Close Combat: Two biggest changes are challenges and the wide disparity between AP2 and AP3. Lots of AP2 weapons that strike at I1, and lots of AP3 weapons that strike at initiative. This creates a very, very interesting dynamic. Challenges are a mini-game that is very interesting to play. 2+ armor feels very powerful now, appropriately so. In general close combat seems much more satisfying and fun.
Highlight of the last game:
Mephiston charged my biker squad which had my Biker Captain with a Relic Blade and Artificer armor. The Biker Captain accepted Meph's challenge and tanked him with his 2+ save. This held Meph in place while I moved up my Land Raider and the next turn charged him with my five Thunder Hammer Storm Shield terminators. Meph challenged, I declined and he sent my Terminator Sargeant to the rear, but my Powerfist bike Sarge and the other four Terminators beat on him (but did not kill him after he made a few 5+ Feel No Pain saves). Next turn he challenged again, I declined, he sent my Termie Sarge to the rear again. He caused multiple wounds on the bike squad, I took them on the Captain again. One got through, he activated his force weapon, and fried my captain. In revenge, Mephiston got beat to a pulp with Thunderhammers.
Armies I'm Going to Run:
I'm thinking of the various army/ally combinations that I would like to run. I think my Loganwing is going to get some Deathwing allies, because TH/SS Terminators with a few more cyclone launchers - that score - would make a STRONG addition to a Footslogging Loganwing. Oh and they can deep strike. Nothing but net. Unfortunately that combo might not last too long as the Dark Angel codex is coming out soonish, but that's fine.
And I have been enjoying the heck out of allying vanilla biker marines with my Grey Knights. Gives them TH/SS Terminators, and fast troops with melta and plasma, which they kind of like.
Tyranids... well double flying Tyrants is a must. The flying Hive Tyrant is my all time favorite 40k model, and one of the reasons I like Tyranids to begin with. It was a shitty choice before, but a better one now. How to support an army around them though... still thinking about it.